Electromagnetic actuator

ABSTRACT

An electromagnetic actuator includes an actuator rod having a plurality of magnetic assemblies disposed about a longitudinal axis of the actuator rod. Each plurality of magnetic assemblies develops alternating magnetic flux along the longitudinal axis. The electromagnetic actuator further includes a plurality of stator windings secured to a support structure and disposed about the longitudinal axis. Each stator winding has a pole facing a portion of one of the plurality of magnetic assemblies and the longitudinal axis.

This is a continuation of application Ser. No. 08/484,866, filed Jun. 7,1995 now U.S. Pat. No. 5,661,446.

BACKGROUND OF THE INVENTION

The present invention relates to linear electrodynamic machines, andmore particularly, to an electromagnetic actuator.

Linear electric motors have increasingly been applied to a number ofapplications where precise displacement is required. Generally, a linearmotor includes a selectively energized winding positioned in closeproximity to a plurality of magnets. In many linear motors, the magnetsare held stationary and the winding is energized so that magnetic fieldscreated by the winding interact with the magnetic fields of thepermanent magnets to cause displacement of the winding relative to thepermanent magnets. In other motors, the magnets are disposed on amovable rod while the stator winding is held stationary.

Recently, there has been interest in replacing conventional hydraulicactuators with linear motors or, more appropriately called,electromagnetic actuators in this application. It is commonly known thatalthough hydraulic actuators can develop high forces, hydraulicactuators typically are just a part of a larger hydraulic system thatrequires other complicated devices such as accumulators, filters andpumps which all must be maintained in order to operate. Furthermore,being that the hydraulic system operates using pressurized fluid, thereis always the risk of a fluid leak.

Although known electromagnetic actuators can provide precise control ofthe moving armature, these actuators have as of yet not replacedhydraulic actuators because sufficient forces comparable to thehydraulic actuators have not yet been obtainable.

SUMMARY OF THE INVENTION

The present invention is an electromagnetic actuator and a method ofmaking the same. The electromagnetic actuator includes an actuator rodhaving a plurality of magnetic assemblies disposed about a longitudinalaxis of the actuator rod. Each plurality of magnetic assemblies developsalternating magnetic flux along the longitudinal axis. Theelectromagnetic actuator further includes a plurality of stator windingssecured to a support structure and disposed about the longitudinal axis.Each stator winding has a pole facing a portion of one of the pluralityof magnetic assemblies and the longitudinal axis. By disposing thestator windings and the magnetic assemblies about the longitudinal axis,forces generated in a plane perpendicular to the longitudinal axis aresubstantially zero, while forces generated from interaction of eachenergized stator winding with its corresponding magnetic assembly addtogether and are parallel to the longitudinal axis.

In a preferred embodiment, the armature is formed of a plurality ofarmature subsections and the magnetic assemblies each comprise aplurality of magnets. Each armature subsection contains a magnet fromeach magnetic assembly. Preferably, each armature subsection is formedof a plurality of armature laminates. The armature laminates are verythin, but when a number of these are stacked and suitably fastenedtogether such as by gluing, each armature subsection, and thus, thearmature itself is very rigid. Each armature laminate includes aperturesspaced-apart at equal angular intervals. The apertures when aligned formcavities that hold the permanent magnets within the armature and,preferably, below an outer surface. The armature outer surface is thenground smooth and plated with electrolysis nickel for corrosionprotection to provide a smooth surface for bearings to slide on.

To minimize the air gap between each stator winding and eachcorresponding magnetic assembly, each stator winding includes a statorpole face that generally conforms to the outer surface of the actuatorrod. Preferably, stator pole faces are laminate structures formed by aplurality of stator pole laminates. The stator pole laminates arepreferably just as thick as the armature laminates. A preferred methodof making the armature laminates and the stator pole laminates so that aprecision air gap results between the outer surface of the actuator rodand stator pole faces includes beginning with a plurality of laminatesthat have an outer portion conforming to the stator pole laminates andan inner portion conforming to the actuator rod laminates. These initiallaminates are then cut, for example by stamping or by laser machining,to form the stator pole laminates and the actuator rod laminates.

In a further preferred embodiment, the armature rod is rotated as wellas displaced linearly. In this preferred embodiment, a conventionalbrushless, direct current, stator winding assembly is disposed aroundthe actuator rod to operate as an electric motor. The actuator rodincludes a second portion having actuator rod subsections constructed inthe manner described above but with magnets of the same polaritydisposed parallel to the longitudinal axis to operate as a conventionalmotor. The second portion of the armature can be lengthened, orpositioned, or additional armature portions can be added to allow thearmature to be rotated at any extended condition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of a first embodiment of anelectromagnetic actuator of the present invention with parts removed;

FIG. 2 is a sectional view of the electromagnetic actuator of FIG. 1taken along lines 2--2;

FIG. 3 is a top plan view of a laminate having a stator pole portion andan armature portion;

FIG. 3A is a top plan view of a stator pole laminate;

FIG. 3B is a top plan view of an armature laminate;

FIG. 4 is a perspective view of a subsection of the actuator rod and aportion of the stator pole face laminates;

FIG. 5 is a sectional view of a stator winding core taken along lines5--5 of FIG. 2;

FIG. 5A is a schematic flat layout view of the stator winding cores ofthe stator assembly with windings and stator pole faces removed;

FIG. 6 is a block and schematic diagram of an actuator controller;

FIG. 7 is a diagrammatic view of three phase windings in a statorwinding core and armature magnets;

FIG. 8 is a longitudinal sectional view of a second embodiment of theelectromagnetic actuator of the present invention with parts removed;

FIG. 9 is a perspective view of a portion of an armature of the secondembodiment;

FIG. 10 is a block and schematic diagram of a motor controller.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates one embodiment of an electromagnetic actuator 10 madein accordance with the present invention. As will be explained andunderstood in the following description, the actuator 10 is selectivelycontrolled for precisely controlling bidirectional displacement of anarmature 12 relative to a stator assembly 14.

Generally, as illustrated in FIG. 2, the electromagnetic actuator 10includes a plurality of stator winding assemblies 16A, 16B, 16C, 16D,16E and 16F spaced at equal angular intervals about a longitudinal axis18. Each stator winding assembly 16A-16F faces a plurality of magneticassemblies 20A, 20B, 20C, 20D, 20E and 20F disposed in the armature 12.As illustrated, the magnetic assemblies 20A-20F are disposed about thelongitudinal axis 18 at the same angular intervals as the stator windingassemblies 16A-16F. Although electromagnets can be used, preferably eachof the magnetic assemblies 20A-20F comprises a bank of permanent magnets22 disposed parallel to the longitudinal axis 18 along a substantialpart of the armature 12 as illustrated in FIG. 1. The poles of eachmagnet 22 are radially disposed so that the corresponding magnetic fieldfrom each magnet 22 extends radially from the longitudinal axis 18.Preferably, the permanent magnets are made of Neodymium-Iron-Boron(NdFeB) material.

As is commonly known, every magnet has two poles designatedconventionally as "N" and "S". FIG. 1 illustrates that the magnets 22 ofmagnetic assemblies 20A and 20D are disposed with alternating polarityalong the longitudinal axis 18. Preferably, the magnets of magneticassemblies 20B, 20C, 20E and 20F are similarly arranged so that asillustrated in FIG. 2, the polarity of the outwardly facing surfaces arethe same about the longitudinal axis 18 for a given position along thelongitudinal axis 18.

Generally, each stator winding assembly 16A-16F and each correspondingmagnetic assembly 20A-20F as a set comprise a linear motor when thestator winding assemblies 16A-16F are suitably energized. By disposingthe stator winding assemblies 16A-16F and the magnetic assemblies20A-20F about the longitudinal axis 18 at equal angular intervals,forces in a plane perpendicular to the longitudinal axis 18 aresubstantially zero, while forces generated from interaction of eachenergized stator winding assembly 16A-16F with its correspondingmagnetic assembly 20A-20F add together and are parallel to thelongitudinal axis 18.

In the preferred embodiment, the armature 12 is tubular having an innerlongitudinal cavity 24. Preferably, the magnets 22 of the magneticassemblies 20A-20F are disposed within the armature 12 below an outersurface 26. The armature 12 is formed of a plurality of armaturesubsections 28 containing a magnet 22 of each magnetic assembly 20A-20F,one of which is illustrated in FIG. 4. Preferably, each armaturesubsection 28 is formed of a plurality of armature laminates 30, one ofwhich is also illustrated in FIG. 3B.

The armature laminate 30 is very thin (approximately 1/16 of an inchthick), but when a number of these are stacked and suitably fastenedtogether such as by gluing, the armature subsection 28 is formed. Itshould be understood that as used herein an "armature laminate" isdefined as having a width less than a width of magnet 22, while a"armature subsection" comprises a plurality of armature laminates 30.Each armature laminate 30 is made of a suitable low reluctance materialsuch as silicon steel.

Referring to FIG. 3B, each armature laminate 30 has the samecross-sectional shape as the subsection 28, and thus the armature 12.The armature laminate 30 includes an inner support portion 32 joined toan outer ring portion 34 with webs 36. The inner support portion 32, theouter ring portion 34 and successive webs 36 define apertures 38 whichare used to hold the magnets 22 as illustrated in FIG. 2 and 4. A notch37 is provided in each armature laminate 30 for aligning the armaturelaminates 30 during assembly of the armature subsection 28. An opening39 is provided in each armature laminate 30 so as to form the opencavity 24 (FIG. 1) when assembled.

Referring back to FIG. 1, the subsections 28 are then glued together toform the armature 12. End caps 38 and 40 are secured at each end. Sincesubsection 28A closest to end cap 38 would not extend under the statorwindings 16A-16F, a suitable filler material 39 can be used in place ofthe magnets 22. Preferably, a suitable fastening device, such as bolts42, extends between the end caps 38 and 40 within the cavity 24 tofurther secure the subsections 28 together. To create the smooth outercylindrical surface 26 on the armature 12, once assembled, the outersurface 26, or more particularly, the outer ring portions 34 (FIG. 3B)of the armature laminates 30 are ground smooth and plated withelectrolysis nickel for corrosion protection to provide a smooth surfacefor bearings 52 and 54 to slide on.

As illustrated in FIGS. 2 and 4, the magnets 22 are separated from eachother and oriented so that the like poles face outwardly and inwardly.It should be understood that tubular shaped magnets (having poles oninner and outer cylindrical surfaces), such as available from DaidoSteel Co. Ltd. of Nagoya 457 Japan can also be used, if desired.

The stator winding assemblies 16A-16F are supported in a housing 44 bycorresponding support blocks 46A, 46B, 46C, 46D, 46E and 46F. Ifdesired, the support blocks 46A-46F can be formed integral with thehousing 44. End caps 48 and 50 are joined to the housing 44 at oppositeends thereof. Apertures 48A and 50A within end caps 48 and 50,respectively, allow the armature 12 to move through the stator assembly14. The bearing elements 52 and 54 are positioned within end caps 48 and50, respectively, and engage the outer surface 26 to guide the armature12 through the stator assembly 14.

Referring to FIGS. 1, 2 and 5, each of the stator winding assemblies16A-16F includes a suitable low reluctance core structure 56A, 56B, 56C,56D, 56E and 56F, respectively. The core structures 56A-56F includerecesses 58 that form teeth 60. In FIG. 1, the windings for statorwinding assemblies 16A and 16D have been removed to illustrate anelevational view of the core structures 56A and 56D. Preferably, eachcore structure 56A-56F comprises a plurality of identical stator corelaminates 62 formed from a suitable low reluctance material such assilicon steel. Referring to FIG. 5, when joined together, the statorcore laminates 62 form a parallelogram structure to provide smootherdisplacement of the armature 12 through the stator assembly 14.

Referring to FIG. 5A, preferably, the orientation of each core structure56A-56F alternates about the longitudinal axis. As appreciated by thoseskilled in the art, the parallelogram structure of the core structures56A-56F will generate a force vector having a substantial vectorcomponent parallel to the longitudinal axis 18 and a smaller vectorcomponent that would tend to rotate the armature 12 about thelongitudinal axis. However, when the core structures 56A and 56F areoriented as illustrated in FIG. 5A about the longitudinal axis, thesmaller vector components will substantially cancel each other out.

To minimize the air gap between each stator winding assembly 16A-16F andeach corresponding magnetic assemblies 20A-20F, each stator windingassembly 16A-16F includes a stator pole face 64A, 64B, 64C, 64D, 64E and64F, respectively. As illustrated, each stator pole face 64A-64Fgenerally conforms to the portion of the outer surface 26 that it faces.The stator pole faces 64A-64F have recesses 68A, 68B, 68C, 68D, 68E and68F that have a width equal to the width of the corresponding corestructures 56A-56F formed by stator core laminates 62. Preferably, thestator pole faces 64A-64F are integrally joined together as illustratedand are formed from a plurality of stator pole laminates 70, one ofwhich is illustrated in FIG. 3A. The stator pole laminates 70 arepreferably just as thick as the armature laminates 30 discussed above. Apreferred method of making the armature laminates 30 and the stator polelaminates 70 so that a precision air gap 71 (FIG. 4) results between theouter surface 26 and the stator pole faces 64A-64F includes beginningwith a plurality of laminates of the shape indicated at 72 in FIG. 3. Asseparated by dashed circle 73, the laminate 72 includes both an innerportion 75 having a shape identical to the armature laminate 30 and anouter portion 77 having a shape identical to the stator pole laminate70. By separating the inner portion 75 from the outer portion 77 alongthe dashed circle 73, for example by stamping or laser machining, anaccurate and consistent air gap 71 can be achieved between the outersurface 26 and the stator pole faces 64A-64F. Although stator corelaminates 62 can be individually extended (indicated by arrow 69 in FIG.2) and/or positioned so that each core structure 56A-56F has an innersurface facing the armature 12 that generally conforms to the outersurface 26 without the use of the stator pole faces 64A-64F, thisstructure would increase the number of unique parts present in theactuator 10 and/or complicate assembly. Instead, since the armaturelaminates 30 are identical to each other, the stator core laminates 62are identical to each other and the stator pole laminates 70 areidentical to each other, the number of individual parts is reduced andassembly is simplified.

It should be understood that the present invention is not limited to theuse of circular armature laminates 30 as herein depicted. For instance,if desired, the armature laminates 30 can have any suitablecross-sectional shape such as but not limited to a triangle, rectangle,hexagon or octagon shape. When the armature laminates 30 and the statorpole laminates 70 are formed from laminates 72 in the manner describedabove, inner surfaces of the stator pole laminates 70 conform to theouter ring portions 34 of the armature laminates 30 to minimize the airgap formed between the armature 12 and the stator pole faces 64A-64F.

Extension of the armature 12 out of the stator assembly 14 is limited bythe end cap 38 striking a suitable bumper 80 provided on the end cap 48.A protective tube 82 extends away from the end cap 48. The protectivetube 82 has an end cap 84 located at its distal end 86. Retraction ofthe armature 12 within the protective tube 82 is limited by contact ofthe end cap 38 upon a bumper 88 joined to an inner surface of end cap84.

FIG. 6 illustrates components of a controller 100 used to energizestator windings 102A, 102B, 102C, 102D, 102E and 102F of stator windingassemblies 16A-16F, respectively. As illustrated, the stator windings102A-120F are connected in a wye or star configuration; however, ifdesired, the stator windings 102A-102F can be connected in a deltaconfiguration.

Generally, the controller 100 is similar to known controllers used inbrushless, direct current, permanent magnet motors. The controller 100includes a rectifier 104 that receives a suitable alternating currentinput signal on signal lines 106 to produce fixed positive and negativeDC voltages on a positive bus 108 and a negative bus 110, respectively.A capacitor 112 is provided to maintain the positive bus 108 and thenegative bus 110 within suitable limits. A three-phase inverter 114 isconnected to the positive bus 108 and the negative bus 110 in aconventional manner to provide three-phase commutated current waveformson power signal lines 116A, 116B and 116C, which are connected to theset of stator windings 102A-102F. The three-phase inverter 114 comprisesa power transistor bridge having solid state transistors 114A, 114B,114C, 114D, 114E and 114F for switching each of the signal lines116A-116C from an open circuit condition to the positive bus 108 or thenegative bus 110. The duty cycle of each transistor 114A-114F iscontrolled by an inverter driver 118, herein illustrated as a logicarray having a look-up table 119 stored in read only memory (ROM). Theinverter driver 118 responds to armature position feedback signalsprovided from a suitable sensor such as an LVDT sensor 120. Preferably,as illustrated in FIG. 1, the sensor 120 is disposed within the cavity24 and mounts at one end to the end cap 84 of the protective tube 82 andat an opposite end to the end cap 40.

Referring back to FIG. 6, an analog-to-digital converter 122 receivesanalog signals from the sensor 120 and converts the signals to a binaryformat suitable for the inverter driver 118. The binary format providesan index into the look-up table 119 to determine which transistors114A-114F should be operated to properly commutate the stator windings102A-102F as a function of the position of the armature 12. It should beunderstood that the inverter driver 118 is but one embodiment forproviding control signals to the transistors 114A-114F. Suitablecombinational logic could also be used instead of the logic array hereindepicted.

FIG. 7 diagrammatically illustrates placement of the three phasewindings (R,S and T) within the recesses 58 of the core structure 56A byway of example. Winding portions 130A indicate the flow of currenttherethrough is into the plane of the drawing, while winding portions132A indicate the flow of current therethrough is out of the plane ofthe drawing.

FIG. 8 illustrates a second embodiment of an electromagnetic actuator150 made in accordance with the present invention. Like the actuator 10described above, the actuator 150 includes an armature 152 that moveslinearly with respect to the a longitudinal axis 158. However, inaddition, the actuator 150 can selectively rotate the armature 152 aboutthe longitudinal axis 158.

The armature 152 includes a first portion 160 having magnets 22 orientedand disposed therein in the manner described above with respect toarmature 12. A stator assembly 164 similar to the stator assembly 14 isdisposed around the longitudinal axis 158 and interacts with the portion160 of the armature 152 to displace the armature 152 parallel to thelongitudinal axis 158.

The actuator 150 also includes a stator assembly 166 conventionallywound to operate as an electric motor. In the embodiment illustrated,the stator assembly 166 forms part of a brushless, direct current,permanent magnet electric motor wherein the armature 152 includes asecond armature portion 168 having magnets 22 oriented conventionally tooperate as an electric motor.

As illustrated in FIG. 9, the armature portion 168 includes threeidentical subsections 168A. 168B and 168C joined together and formedfrom armature laminates 30 in the manner described above. Asillustrated, the magnets 22 of the armature 168A-168C are disposed withalternating polarity about the longitudinal axis 158, while magnets ofthe same polarity are disposed parallel to the longitudinal axis 158.

The armature portion 168 is joined to the armature portion 160 with afirst tubular member 170, while a second tubular member 172 extendstoward an end cap 174. The tubular members 170 and 172 can be solidtubes or can be formed from armature laminates 30 having suitablefillers used in place of the magnets 22. Extension of the armature 152out of the stator assembly 164 is limited by the end cap 174 engaging asuitable bearing element 175 mounted to the armature 152. The bearingelement 175 allows rotation of the armature 152 about the axis 158 whendesired. As appreciated by those skilled in the art, the bearing element175 can also be mounted to the end cap 176 if desired. A protective tube180 extends away from the end cap 176. The protective tube 180 has anend cap 182 located at its distal end 184. Retraction of the armature152 within the protective tube 180 is limited by contact of the end cap174 with a bumper 189 joined to an inner surface of the end cap 182.

The stator assembly 166 is connected to a suitable motor controller 190through lines 192A, 192B, 192C. The motor controller 190 is similar tothe actuator controller 100 described above, accordingly, likecomponents have been similarly numbered. A resolver-to-digital converter200 receives analog signals from a resolver 202 and converts the signalsto a binary format suitable for the inverter driver 118 of the motorcontroller 190. The binary format provides an index into a look-up table191 to determine which transistors 114A-114F should be operated toproperly commutate the stator windings 166 as a function of the angularposition of the armature 12. It should be understood that the resolver202 is but one embodiment for sensing the angular position of thearmature 152. Any suitable sensor such as an encoder or Hall effectsensors could also be used.

Referring back to FIG. 8, the actuator 150 displaces the armature 152along the axis 158 as well as rotates the armature 152 about the axis158. In the embodiment illustrated, when the armature 152 is fullyextended, the armature portion 168 is aligned with the stator assembly166 to allow operation of the motor thereof to rotate the armature 152.It should be understood that the armature portion 168 can be lengthened,or positioned, or additional armature portions 168 can be added to allowthe armature 152 to be rotated at any extended condition.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

What is claimed is:
 1. An electromagnetic actuator comprising:anactuator rod comprising:a first plurality of magnetic assembliesdisposed about a longitudinal axis of the actuator rod, wherein themagnetic assemblies are disposed to develop alternate magnetic fluxalong the longitudinal axis; a second plurality of magnetic assembliesdisposed about a longitudinal axis of a second portion of the actuatorrod, wherein the magnetic assemblies develop alternate magnetic fluxabout the longitudinal axis; a support structure; a first plurality ofstator winding assemblies secured to the support structure and disposedabout the longitudinal axis, the first plurality of stator windingassemblies being operable with the first plurality of magneticassemblies to move the actuator rod longitudinally along thelongitudinal axis from a first position to a second position; and asecond plurality of stator winding assemblies secured to the supportstructure and disposed about the longitudinal axis, the second pluralityof stator winding assemblies being operable with the second plurality ofmagnetic assemblies to rotate the actuator rod about the longitudinalaxis when the actuator rod is in the second position.
 2. Theelectromagnetic actuator of claim 1 wherein the first plurality ofstator winding assemblies comprises at least one stator winding isstaggered relative to the other stator windings along the longitudinalaxis.
 3. The electromagnetic actuator of claim 1 wherein the firstplurality of stator winding assemblies comprises a set of three phasewindings.
 4. The electromagnetic actuator of claim 1 wherein the secondplurality of stator winding assemblies comprises a set of three phasewindings.
 5. The electromagnetic actuator of claim 1 wherein eachmagnetic assembly comprises a plurality of magnets.
 6. Theelectromagnetic actuator of claim 1 and further comprising:a firstcommutation circuit connected to the first plurality of stator windingassemblies; and a second commutation circuit connected to the secondplurality of stator winding assemblies.